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Overview
Comment:Consider doing a partial table scan to fulfill an IN operator rather than using an index. Try to pick the plan with the lowest cost.
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SHA3-256:1fa40a78fef4516c39b217bff67efe7e7d2077cca00aae0ef5c2c9cff94f008b
User & Date: drh 2018-06-08 18:22:10
Context
2018-06-08
19:54
Merge the btreeNext() assertion bug fix from trunk. check-in: 11bd66e0 user: drh tags: in-scan-vs-index
18:22
Consider doing a partial table scan to fulfill an IN operator rather than using an index. Try to pick the plan with the lowest cost. check-in: 1fa40a78 user: drh tags: in-scan-vs-index
2018-06-07
18:13
The IN-early-out optimization: When doing a look-up on a multi-column index and an IN operator is used on a column other than the left-most column, then if no rows match against the first IN value, check to make sure there exist rows that match the columns to the right before continuing with the next IN value. check-in: 09fffbdf user: drh tags: trunk
Changes
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Changes to src/where.c.

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        || (pNew->wsFlags & WHERE_COLUMN_NULL)!=0 
        || (pNew->wsFlags & WHERE_COLUMN_IN)!=0 
        || (pNew->wsFlags & WHERE_SKIPSCAN)!=0 
    );

    if( eOp & WO_IN ){
      Expr *pExpr = pTerm->pExpr;
      pNew->wsFlags |= WHERE_COLUMN_IN;
      if( ExprHasProperty(pExpr, EP_xIsSelect) ){
        /* "x IN (SELECT ...)":  TUNING: the SELECT returns 25 rows */
        int i;
        nIn = 46;  assert( 46==sqlite3LogEst(25) );

        /* The expression may actually be of the form (x, y) IN (SELECT...).
        ** In this case there is a separate term for each of (x) and (y).
................................................................................
        }
      }else if( ALWAYS(pExpr->x.pList && pExpr->x.pList->nExpr) ){
        /* "x IN (value, value, ...)" */
        nIn = sqlite3LogEst(pExpr->x.pList->nExpr);
        assert( nIn>0 );  /* RHS always has 2 or more terms...  The parser
                          ** changes "x IN (?)" into "x=?". */
      }






























    }else if( eOp & (WO_EQ|WO_IS) ){
      int iCol = pProbe->aiColumn[saved_nEq];
      pNew->wsFlags |= WHERE_COLUMN_EQ;
      assert( saved_nEq==pNew->u.btree.nEq );
      if( iCol==XN_ROWID 
       || (iCol>=0 && nInMul==0 && saved_nEq==pProbe->nKeyCol-1)
      ){







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        || (pNew->wsFlags & WHERE_COLUMN_NULL)!=0 
        || (pNew->wsFlags & WHERE_COLUMN_IN)!=0 
        || (pNew->wsFlags & WHERE_SKIPSCAN)!=0 
    );

    if( eOp & WO_IN ){
      Expr *pExpr = pTerm->pExpr;
      LogEst M, logK;
      if( ExprHasProperty(pExpr, EP_xIsSelect) ){
        /* "x IN (SELECT ...)":  TUNING: the SELECT returns 25 rows */
        int i;
        nIn = 46;  assert( 46==sqlite3LogEst(25) );

        /* The expression may actually be of the form (x, y) IN (SELECT...).
        ** In this case there is a separate term for each of (x) and (y).
................................................................................
        }
      }else if( ALWAYS(pExpr->x.pList && pExpr->x.pList->nExpr) ){
        /* "x IN (value, value, ...)" */
        nIn = sqlite3LogEst(pExpr->x.pList->nExpr);
        assert( nIn>0 );  /* RHS always has 2 or more terms...  The parser
                          ** changes "x IN (?)" into "x=?". */
      }
      /* Let:
      **   N = the total number of rows in the table
      **   K = the number of entries on the right-hand side of the IN operator
      **   M = the number of rows in the table that match terms to the 
      **       to the left in the same index.  If the IN operator is on
      **       the left-most index column, M==N.
      **
      ** Given the definitions above, it is better to omit the IN operator
      ** from the index lookup and instead do a scan of the M elements,
      ** testing each scanned row against the IN operator separately, if:
      **
      **        M*log(K) < K*log(N)
      **
      ** Our estimates for M, K, and N might be inaccurate, so we build in
      ** a safety margin of 2 (LogEst: 10) that favors using the IN operator
      ** with the index, as using an index has better worst-case behavior.
      */
      M = pProbe->aiRowLogEst[saved_nEq+1];
      logK = sqlite3LogEst(nIn);
      if( M + logK + 10 < nIn + rLogSize ){
        WHERETRACE(0x40,
          ("IN operator costs more than scan on column %d of \"%s\" (%d<%d)\n",
           saved_nEq, pProbe->zName, M+logK+10, nIn+rLogSize));
        continue;
      }else{
        WHERETRACE(0x40,
          ("IN operator cheaper than scan on column %d of \"%s\" (%d>=%d)\n",
           saved_nEq, pProbe->zName, M+logK+10, nIn+rLogSize));
      }
      pNew->wsFlags |= WHERE_COLUMN_IN;
    }else if( eOp & (WO_EQ|WO_IS) ){
      int iCol = pProbe->aiColumn[saved_nEq];
      pNew->wsFlags |= WHERE_COLUMN_EQ;
      assert( saved_nEq==pNew->u.btree.nEq );
      if( iCol==XN_ROWID 
       || (iCol>=0 && nInMul==0 && saved_nEq==pProbe->nKeyCol-1)
      ){